The residents of the study area, approximately 8000 people aged at least 5 years, have participated in a longitudinal population study since 1965, allowing study of the risk factors and effects of diabetes mellitus. Long-term observations, up to 40 years, confirmed the profound effect of pre-existing diabetes or abnormal glucose tolerance in pregnancy on the risk of diabetes in the offspring. Among nondiabetic children, a number of risk factors, including parental diabetes, body size measurements and glucose and insulin concentrations, predict development of diabetes by young adulthood. Individual estimates of risk can be made to assist in identifying children and adolescents at highest risk of developing diabetes so that more intensive intervention can be offered. Largely due to increasing obesity in children and the vicious cycle of increasing prevalence of diabetes in pregnancy, the incidence of type 2 diabetes in Pima Indian children and adolescents has increased dramatically over the last few decades, despite relatively little change in incidence rates in adults. Increasing prevalence of type 2 diabetes in youth leads to long-term complications such as renal failure occurring in middle adulthood and perpetuates the vicious cycle of diabetes in pregnancy begetting diabetes in the offspring.